1. Field of the Invention
The present invention primarily relates to an external storage device system for computers, and especially to a technology for improving the performance of a magnetic disk array system (hereafter called “magnetic disk array device”).
2. Description of the Related Arts
A conventional technology in which a magnetic disk array device (RAID device: Redundant Arrays of Inexpensive Disks device) records data with high reliability and at high-speed by distributing data processing and recording redundant data among a plurality of disks is widely used.
Generally, magnetic disk array devices have numerous disks mounted, and a disk array controller, which is an input/output control device, is mounted to store and process data appropriately distributed in and among the magnetic disks.
In addition to a function for performing a processing to store data in appropriate disks, the disk array controller also has a function to format a plurality of disks for RAID purposes, a function to calculate and write redundant data to prevent data loss even in the unlikely event of disk failure, and a failure preventive function to detect disks with signs of failure before failures occur; the disk array controller performs numerous control processing besides input/output to and from magnetic disks. For this reason, the disk array controller is required to have the performance to process data at high-speed, and improvements have been made to this end.
In the meantime, as another method for achieving high performance in the magnetic disk array device, there is an offload processing (a processing to remove load from the disk controller), wherein, instead of having the disk array controller handle all the processing, sub-controllers that are subordinate to the disk array controller are provided and a part of the processing is handled by the sub-controllers.
As a method for achieving high-speed processing through offload processing, multiple executions of a plurality of formats are performed by dividing a Fibre Channel loop into a plurality of loops and using a sub-controller provided for each loop.
By dividing the Fibre Channel loop through which data travels, data that travels on the loops can be localized and usage efficiency of a data bus of the controller can be improved. Further, it is possible to reduce I/O processing load on the controller by having the sub-controllers perform a part of the processing previously done by the controller. Moreover, processing such as copying between disks and online verification, which is a type of preventive maintenance, for checking the surface of disks online without stopping the device, can be done.